1. Field of the Invention
This invention relates to gas discharge type pile driving hammers which can operate under water and in particular it concerns improvements providing control of liquid purge and reflooding in such hammers for improving the efficiency thereof.
2. Description of the Prior Art
Prior art gas discharge type underwater hammers are shown and described in U.S. Pat. No. 3,958,647 to Stephen V. Chelminski. Other patents in this field are U.S. Pat. Nos. 3,604,519; 3,646,598; 3,714,789; 3,721,095; 3,788,402; 3,817,335 and 3,892,279. In addition, there are two pending U.S. patent applications known to applicant which relate to gas discharge type underwater hammers. These are application Ser. No. 745,637 filed Nov. 29, 1976 and now U.S. Pat. No. 4,060,139 in the name of Harold Lee Adair and application Ser. No. 763,085 filed Jan. 27, 1977 in the name of George J. Gendron and Henry A. Nelson Holland, both of which applications are assigned to the assignee of the present invention.
In general, a gas discharge type underwater hammer comprises an elongated guide tube, a massive ram that is driven up and down in the tube, an anvil in the tube which is hammered upon by the ram and a gas discharge device positioned between the ram and the anvil. When the gas discharge device is triggered, it releases a charge of highly compressed gas which drives the ram upwardly in the guide tube. When the pressure of the gas dissipates and the ram loses its upward momentum it falls back onto the anvil; and the striking force of the ram on the anvil drives the pile, or other element on which the anvil is mounted, downwardly. The gas which is used to drive the ram upwardly in the guide tube is exhausted from the hammer during each cycle through an annular clearance between the ram and the guide tube; and the region under the ram is reflooded prior to the next gas discharge by a flow of water down through a central passageway in the ram. In one prior art gas discharge type hammer a gas reservoir is arranged to be placed into communication with the interior of the ram guide tube under the ram after the ram has been driven upwardly. The space between the ram and guide tube above the region of communication is essentially sealed to prevent passage of the gas which is used to drive the ram upwardly in the guide tube. This gas then exhausts into the reservoir and is thereby prevented from aerating the incoming water which refloods the region under the ram.